在Python中模拟事件

首先，什么是事件？
事件是使一个类能够在感兴趣的事情发生时通知其他类的构造。
在通俗的语言中，它基本上类似于举起旗帜来向其他人表示感兴趣的事情发生了。

何时在Python中使用事件？

基于事件的编程主要在使用 UI（用户界面）时使用，其中不同的组件需要发出某些事件的信号。例如，想象一个货币转换器需要在 box2 中输出转换后的货币，而用户在 box1 中输入一些值。
box2 如何知道用户在 box1 中输入了一些内容，以及在响应中需要做什么。
这是基于事件的编程最基本的例子之一。
另一个可能的例子是家庭安全系统，其中一些可能的动作，例如需要发出警报，需要将消息发送给所有者，并且需要通知警方关于可能的盗窃将在违反锁。这些类型的系统可以使用基于事件的机制轻松设计，一旦有人打破锁，就会引发事件，然后通知事件处理程序发挥他们的作用。
现在，在这篇文章中，我们将使用后一个示例来了解如何在默认情况下不支持的Python中设计此类事件。

Python3

class Event(object):
 
    def __init__(self):
        self.__eventhandlers = []
 
    def __iadd__(self, handler):
        self.__eventhandlers.append(handler)
        return self
 
    def __isub__(self, handler):
        self.__eventhandlers.remove(handler)
        return self
 
    def __call__(self, *args, **keywargs):
        for eventhandler in self.__eventhandlers:
            eventhandler(*args, **keywargs)
                 
class Police(object):
    def __init__(self, policeTelephoneNo):
        self._telephone = policeTelephoneNo
     
    def CallPolice(self):
        print ("police have been informed")
 
class Owner(object):
    def __init__(self, ownerMobile):
        self.__mobile = ownerMobile
     
    def Message(self):
        print ("owner has been messaged about the possible theft")
         
class Alarm(object):
     
    def StartAlarm(self):
        print ("Alarm has started")
         
# LockClass
 
class Lock(object):
     
    def __init__(self):
        self.OnLockBroken = Event()
         
    def LockBroken(self):
        # This function will be executed once a lock is broken and will
        # raise an event
        self.OnLockBroken()
         
    def AddSubscribersForLockBrokenEvent(self,objMethod):
        self.OnLockBroken += objMethod
         
    def RemoveSubscribersForLockBrokenEvent(self,objMethod):
        self.OnLockBroken -= objMethod
 
def Simulation():
    # In the simulation we have a lock
    # which will be broken and the object of Police
    # owner and Alarm classes which are
    # to be notified as soon as lock is broke
     
    # Required objects
    godrejLockObj = Lock()
    localPoliceObj = Police(100)
    ownerObj = Owner(99999999)
    mainDoorAlarmObj = Alarm()
     
    # Setting these objects to receive the events from lock
    godrejLockObj.AddSubscribersForLockBrokenEvent(localPoliceObj.CallPolice)
    godrejLockObj.AddSubscribersForLockBrokenEvent(ownerObj.Message)
    godrejLockObj.AddSubscribersForLockBrokenEvent(mainDoorAlarmObj.StartAlarm)
     
    # Now the Lock is broken by some burglar
    # thus LockBroken function will be called
    godrejLockObj.LockBroken()
     
    # All three notifications must be printed
    # as soon as Lock is broken now
     
    # You can also remove any receiver by
    # calling the RemoveSubscribersForLockBrokenEvent
    godrejLockObj.RemoveSubscribersForLockBrokenEvent(mainDoorAlarmObj.StartAlarm)
if __name__ == "__main__":        
    Simulation()

输出：

police have been informed
owner has been messaged about the possible theft
Alarm has started